Rising oil prices caused by increasing demand and diminishing supply of crude oil call for the development of alternative ways to supply sustainable fuels and chemicals. In addition, an ever-increasing reliance on foreign oil coupled with political instability in oil-rich countries may jeopardize the fulfillment of domestic energy demands. The effect of high crude oil prices on different sectors of national economies is profound, especially in the transportation sector, which relies heavily on petroleum-derived fuels. Simply put, at present there is no practical alternative to fossil fuels. The aviation industry has recently seen drastic changes in its operating costs. Recently (early 2007), U.S. airline officials noted that jet fuel makes up 30% of long-haul operating costs for airlines, compared with 12-15% two years ago. Indeed, although turbine engines are much more fuel tolerant than gasoline and diesel engines, the engine and fuel systems in jets are more sensitive to the physical and chemical properties of the fuel. Therefore, jet fuel quality is critical to safety, and strict specifications are used to limit the range of fuel properties to insure proper performance during all stages of flight. The large number of physical and chemical properties that must be controlled to produce a fuel that will perform consistently make jet fuel the most rigidly controlled product produced by oil refiners, thereby also making it much more sensitive to price fluctuations.
Many of the stringent requirements of jet fuel are achieved by controlling the fuel composition. Freezing point, combustion properties, thermal oxidation stability, viscosity, and gum formation are significantly influenced by the types and amounts of hydrocarbons in the fuel. Aliphatic hydrocarbons are the primary hydrocarbon components (81%) of jet fuels, and exhibit a range of carbon chain lengths primarily between C8 and C17 (9% C8-C9, 65% C10-C14, and 7% C15-C17). Therefore, one of the main challenges for non-petroleum jet fuel alternatives is efficiently to attain a hydrocarbon composition in this range. For the mandated specifications for jet fuel, see, for example, Yan et al. (2005) “Aviation Turbine Fuel Specifications and Test Methods,” Energy & Fuels 19: 1804-1811.
Biomass, an abundant renewable resource that can substitute for a significant fraction of the energy used worldwide, represents the only sustainable source of carbon for renewable liquid fuels. However, obtaining liquid fuels from biomass not only requires the development of novel processing techniques to selectively break down its highly oxygen-functionalized molecules, but it also requires converting them into molecules with the necessary physical and chemical properties. For example, the Roadmap for Biomass Technologies in the United States (U.S. Department of Energy, Accession No. ADA436527, December 2002), authored by 26 leading experts, has predicted a gradual shift from a petroleum-based economy to a more carbohydrate dependent economy. This official document predicts that by 2030, 20% of transportation fuel and 25% of chemicals consumed in the United States will be produced from biomass. Such a shift away from petroleum-based technologies requires developing innovative, low-cost separation and depolymerization processing technologies to break down the highly oxygen-functionalized, polysaccharide molecules found in raw biomass, to yield useful bio-derived materials and fuels. In short, abundant biomass resources can provide alternative routes for a sustainable supply of both transportation fuels and valuable intermediates (e.g., alcohols, aldehydes, ketones, carboxylic acid, esters) for production of drugs and polymeric materials. However, unless these alternative routes can be implemented at a production cost roughly comparable to the corresponding production cost when using petroleum feedstocks, the transition will inevitably be accompanied by severe economic dislocations. It is not enough that the transition can be accomplished; to avoid economic upheaval, the transition must be accomplished in an economically feasible fashion.
The present invention provides an economically feasible process for producing transportation fuels from biomass-derived oxygenated hydrocarbons.